WO2024117955A1

WO2024117955A1 - Cutting blade

Info

Publication number: WO2024117955A1
Application number: PCT/SE2023/051086
Authority: WO
Inventors: Olle HJELMÅKER
Original assignee: Husqvarna Ab
Priority date: 2022-12-02
Filing date: 2023-10-31
Publication date: 2024-06-06
Also published as: SE2251407A1

Abstract

A lawn mower cutting blade (3) comprises a cutting edge (5) and an attachment opening (9). The attachment opening (9) has a mounting portion (11) and at least one working portion (10). The mounting portion (11) is open on a side edge (6, 14) of the cutting blade. A mounting pin (4), for holding the cutting blade (3) has a narrow section (13) and a wide section (12). The mounting pin (4) is movable in its longitudinal extent against a bias from a biasing means (7). The cutting blade (3) is rotatable on the wide section (12) of the mounting pin (12) and manually slideable past the narrow section (13) thereof. In a mounting method, the mounting pin (4) is moved axially, such that its narrow section (13) is accessible, the narrow portion (13) is introduced into the mounting portion (11) and into the working portion (10). Then the mounting pin (4) is moved axially, such that its wide section (12) is arranged in the working portion (10).

Description

CUTTING BLADE

Field of the invention

The present invention relates to a grass cutting blade for a robotic lawn mower, the cutting blade being elongate with two longitudinal side edges and comprising at least one cutting edge on at least one of the longitudinal side edges of the cutting blade and at least one attachment opening in an area between the longitudinal side edges, and the attachment opening has a mounting portion and at least one working portion.

The invention further relates to a mounting pin, for holding the above- mentioned cutting blade, the mounting pin having a narrow section with a smallest transverse dimension, a wide section with a larger transverse dimension.

In a third aspect, the invention relates to a combination of at least one mounting pin as above, and a cutting disk for a robotic lawn mower.

In a fourth aspect, the invention relates to a combination of at least one cutting blade as above, and at least one mounting pin as above.

In a fifth aspect, the invention relates to a robotic lawn mower including a cutting blade as above, or a mounting pin as above or a combination as above.

In a sixth aspect, the invention relates to a mounting method of a cutting blade as above on a cutting disk of a robotic lawn mower, comprising a mounting pin as above.

EP3102021 B1 discloses a robotic work tool, wherein a plate spring is arranged to hold a cutting blade in position on a cutting disk. The cutting blade has a hole which is large enough to accommodate an attachment pin, such as a screw, around which the cutting blade is rotatable. The plate spring is arranged to be biased towards the cutting disk, with the cutting blade inside of it, i. e. closer to the cutting disk, to keep the blade in its place on the attachment pin. Although the mounting and demounting of the cutting blade is indeed possible without tools, it may be complicated to use in practice. The bias of the blade spring is critical, in order to obtain a construction which holds the cutting blade securely and yet allowing for a rotation. Bending the blade springs too far to release the cutting blade may affect their biasing function. The cutting blade may then be unable to fulfil their original function, and may have to be exchanged, If the bias is too high, the cutting blade will not be able to rotate as intended around the attachment pin. Demounting the springs without bending them may be a solution to these problems, but that may be a complicated and non-intuitive step during the exchange of the cutting blade.

Summary

It is an object of the present invention to solve, or at least mitigate, parts or all of the above-mentioned problems. To this end, there is provided a cutting blade wherein the mounting portion extends between the working portion and a side edge of the blade and is open on said side edge.

Hereby the cutting blade may be mounted and demounted on the robotic lawn mower without the use of tools. Yet the blade will remain secured in the robotic lawn mower during its operation.

The size of the blade is such that its side edges are in the interval of 15-60 mm. Its thickness may be dependent of the properties of the material used, but typically it is in the interval of 0.3-1 .5 mm.

In some cases, the cutting blades may be embossed for a stiffening purpose, e. g. around an opening in the blade or as ridges. The outer dimensions of the blade in the thickness direction may increase, even though the thickness of the actual material does not. However, the outer dimension in the thickness direction rarely exceeds 3 mm. The weight of each blade may be in the interval of 1 -5 g.

Materials that may be used in the cutting blades may, for instance be stainless steel, other steel alloys, titanium, etc. Some blades may be coated, or otherwise surface treated, with additional materials. Preferably, a largest width of the working portion is larger than a width of the mounting portion.

Hereby the cutting blade may be pivotably and securely arranged on a mounting pin extending through the working portion. The working portion has a width which is slightly larger than the pin whereon it is mounted to enable a pivoting thereon. However, the width of the mounting portion is smaller than the width of the working portion, at least in a transition zone between the working portion and the mounting portion. Hereby the width of a pin corresponding to the width of the working portion may not unintentionally pass, or be passed, from the working portion into mounting portion. The cutting blade will hence remain securely installed on a pin with such a width.

In one embodiment of the cutting blade, both longitudinal sides of the blade are provided with cutting edges.

Hereby the cutting blade may be cutting efficiently regardless of the direction of rotation of a cutting disk whereon it may be mounted.

In some embodiments the cutting blade comprises at least one transversal side edge, extending between the longitudinal side edges.

Hereby there may be a side edge without a cutting edge. Such an edge may advantageously lend itself to the opening of the mounting portion, such that neither of the cutting edges may not be shortened.

In some embodiments the mounting portion of the attachment opening is defined by a pair of mutually opposing mounting portion edges.

Hereby the edges of the mounting portion may serve the purpose of directing the motion of the cutting blade relative to a mounting pin in such a direction that the pin ends up in the working portion of the attachment opening. One condition is that the width of the mounting pin is small enough to pass the whole mounting portion and into the working portion.

In some embodiments the at least one attachment opening comprises one single working portion and one single mounting portion, respectively. Hereby the mounting may be as simple and intuitive as possible. Since the mounting is intended to take place without any tools, it is also advantageous that it may be performed easily without any requirements for special skills of the operator.

In some further embodiments the mounting portion of the attachment opening has elongated sides extending parallel to the longitudinal sides of the blade.

Hereby the direction of the movement needed to mount the blade should be clear even to an unskilled operator as well as under adverse conditions, wherein the visibility of the blade is reduced or obscured.

In some even further embodiments, the attachment opening is arranged symmetrically on a center line midway between the two longitudinal side edges.

Hereby the cutting blade may acquire symmetrical properties, and the orientation of the blade may be irrelevant. This, in turn, ensures that the cutting blade may be mounted in a correct position, regardless of its orientation. Also, the symmetry contributes to a well-balanced cutting blade, and, in the end, an excellent mowing result.

In some embodiments the working portion has elongated sides, and the mounting portion is joined to the working portion on an elongated side thereof.

Hereby the risk of wear from the mounting pin on the opening of the mounting portion into the working portion is reduced. Such wear could otherwise widen the opening, and the wide section of the mounting pin could unintentionally pass therethrough. Instead, the mounting pin may primarily contact the ends of the working portion, and the elongated sides may be spared.

In some embodiments at least one of the mounting portion and the working portion is arranged with an angle between a respective axis of extent and the longitudinal side edges of the cutting blade.

Hereby the cutting blade may be well balanced during working, due to a well distributed weight, while the wear on the opening between the mounting portion and the working portion is limited. In still further embodiments, the cutting blade comprises two attachment openings, arranged at opposing side edges of the blade, with their mounting portions open towards their respective adjacent side edge of the cutting blade.

Hereby the cutting blade may be mountable with two different orientations, depending on which attachment opening is used for the mounting. The lifespan of the cutting blade may be extended since the blade is turnable and all of the cutting edges may be utilized.

In a further embodiment, the attachment openings are symmetrically arranged about a longitudinal center of the cutting blade.

Hereby the weight distribution of the blade may be even, and the cutting blade may be well balanced during working, resulting in a well-cut lawn.

In some embodiments the attachment openings are arranged radially symmetrically around a center of the cutting blade.

Hereby a reversible, well balanced cutting blade may be obtained.

In some embodiments each attachment opening has an axis of extent forming an angle to a center line midway between the two longitudinal side edges of the cutting blade.

Hereby further possibilities are given to create a cutting blade with a suitable weight distribution, a secure mounting and possibly with an attractive visual appearance.

In some embodiments a protective member is removably arranged on the cutting blade, covering at least a part of the transversal side across the mounting portion, while exposing at least a part of the cutting edge.

Hereby the cutting blade may be more secure to handle manually, while largely maintaining its cutting properties.

According to a second aspect, parts or all of the above-mentioned problems are solved, or at least mitigated, by a mounting pin wherein an end stopper is arranged at each end of the mounting pin. Hereby the cutting blade may be mounted on the mounting pin at the narrow section, which may pass through the mounting portion and into the working portion. The wide section of the mounting pin is unable to make such a passage. Hence, when the pin has entered the working portion, by a relative motion between the cutting blade and the mounting pin, and the cutting blade is transferred to a position where the wide part of the mounting pin extends through the mounting portion, the cutting blade is securely mounted on the mounting pin. One condition for the secure mounting is, of course, that the cutting blade does not reach the level of the narrow portion until it is to be demounted.

In a further embodiment, the mounting pin comprises two joinable parts.

Hereby the mounting pin may easily be arranged on a cutting disk without the need for special tools. Also, the mounting pin may be exchanged, as a spare part, separately from the cutting disk.

In a still further embodiment, one part of the mounting pin is provided with a socket, and the other part of the mounting pin comprises a projection, which is insertable into the socket.

Hereby a practical way is attained of constructing a mounting pin comprising two joinable parts.

In some embodiments the narrow section is arranged at a central portion of the mounting pin.

Hereby the mounting pin may preferably be moved in either direction to conceal the narrow section so that the cutting blade does not reach that level during operation of the lawn mower. For example, the mounting pin may be moved in its longitudinal direction, so that the narrow section is positioned at the level of the cutting disk whereon the mounting pin is arranged. In some embodiments, the mounting pin may be slid longitudinally to a position where the cutting blade is arranged on the wide section on one side of the cutting disk while the narrow section is arranged on the other side.

In some embodiments the mounting pin comprises a bias spring arranged thereon. Hereby the mounting pin may be biased to attain and remain in a position suitable for operation of the lawn mower. This would be a position wherein the cutting blade is arranged securely on the wide section of the mounting pin, without the possibility of accidentally moving to the level of the narrow section.

In the third aspect of the invention the mounting pin is arranged on the cutting disk, approximately perpendicular to a main plane of extension of the cutting disk, and a biasing means is arranged on the cutting disk and contacting the mounting pin, such that the mounting pin is movable in its longitudinal extent against a bias from the biasing means.

Hereby there are several options for concealing the narrow section of the mounting pin, e. g. by the thickness of the cutting disk or by being on the opposite side of the cutting disk as seen from the intended position of the cutting blade. Simultaneously the mounting pin is still movable to a position wherein mounting or demounting of a cutting blade is possible, by pressing or pulling on an end thereof in a direction opposite the bias.

In the fourth aspect of the invention the mounting pin is arranged on a cutting disk for a robotic lawn mower, which cutting disk has a main plane of extension, and the cutting blade is arranged to be rotatable on the wide section of the mounting pin around a rotational axis defined by a longitudinal extent of the mounting pin, which is extending in a direction across the main plane of extension of the cutting disk, the mounting pin and the cutting blade are mutually movable in the direction of the rotational axis, and the cutting blade is manually slideable past the narrow section of the mounting pin.

Hereby it is clear that a relative movement between the cutting blade and the mounting pin determines the ability to mount and demount the cutting blade. It is immaterial which component is actually moving from an external point of view, as long as the relative movement of the cutting blade and the mounting pin is sufficient to bring them into a position where the attachment opening on the cutting blade is positioned at the level of the narrow portion of the mounting pin. In such a position a mounting and a demounting of the cutting blade to/from the mounting pin is enabled. In a further embodiment of the fourth aspect, the cutting blade is slideable past the narrow section of the mounting pin by a motion transversal to the rotational axis.

Hereby the mounting pin and the cutting blade may perform a relative motion where the mounting pin may pass the mounting portion of the attachment opening and into the working portion or vice versa.

In some embodiments, the mounting pin is movable in its axial direction by manual force.

Hereby the mounting pin may be pressed or pulled in its axial direction to expose its narrow section, and the cutting blade may be mounted or demounted in a toolless manner.

In some embodiments a biasing means is arranged on the cutting disk, and the mounting pin and the biasing means are mutually movable in the longitudinal extent of the mounting pin against a bias from the biasing means.

Hereby a mounting pin which automatically returns to a position where its narrow section is inaccessible is accomplished. Manual manipulation may be needed to expose the narrow section for mounting or demounting of the cutting blade, but on release, the mounting pin resumes its working position.

In some embodiments, the narrow section may be constantly seen, but not accessible, unless a biasing means has been temporarily moved manually to make the narrow section accessible. In this position, the cutting blade may be mounted or demounted. When the biassing means is released, it moves relative to the mounting pin, so that the narrow section is no longer accessible for mounting or demounting of the cutting blade.

In further embodiments the biasing means contacts at least one of the end stoppers on the mounting pin.

Hereby an arrangement wherein a pressure spring is arranged around the mounting pin in contact with one end stopper at one end and with the cutting disk at the other end is enabled. When the end stopper is pressing against the spring, against its spring action, the narrow portion of the mounting pin may be accessible. After the mounting or demounting of the cutting blade, the end stopper is released, and the pressure spring may bring the mounting pin back to its original position, i. e. the working position.

In another embodiment, the biasing means may be a leaf spring which is attached to the cutting disk at one end and which contacts the end stopper at the other end. When the mounting pin is manually pressed against the action of the leaf spring, the narrow portion of the mounting pin may be accessible, as mentioned above. When the mounting or demounting of the cutting blade has been completed, the released mounting pin may be brought back to its working position by the action of the leaf spring.

In some embodiments the cutting blade is arranged below the cutting disk, as seen in an operating position.

Hereby the mounting and demounting of the cutting blade on each mounting pin may be performed easily.

In some other embodiments, the cutting blade is arranged above the cutting disk, as seen in an operating position.

Hereby the cutting blade may be, at least partially, protected from dirt and grass clippings, so that it may yield and rotate easily around the axis of rotation defined by the mounting pin.

In an embodiment of the mounting method, it comprises the following steps: the mounting pin is moved in its axial direction, such that its narrow section is accessible, the cutting blade is brought to the mounting pin with its open mounting portion facing the mounting pin and the cutting blade is held with its main plane of extent at the level of the narrow section of the mounting pin, the cutting blade is moved, at the same level, relative to the mounting pin, such that the narrow portion is introduced first into the mounting portion and then into the working portion, whereafter the mounting pin is moved in its axial direction, such that its wide section is arranged at the level of the cutting blade in the working portion.

Hereby the cutting blade may be mounted and demounted manually, without the use of any tools. In a further embodiment of the mounting method, the mounting pin is moved against a bias in at least one of its axial directions.

Hereby the mounting pin may revert to its working position, by the action of the biassing force, as soon as the mounting pin is released.

It is noted that embodiments of the invention may be embodied by all possible combinations of features recited in the claims. Further, it will be appreciated that the various embodiments described for the device are all combinable with the method as defined in accordance with the second aspect of the present invention, and vice versa.

Brief description of the drawings

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and nonlimiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:

Fig. 1 is a diagrammatic view from above of a robotic lawnmower according to the disclosure;

Fig. 2a is an exploded view in perspective of a portion of the cutting disk in the lawnmower according to Fig. 1 ;

Fig. 2b is a schematic view from the side of a cutting blade on a mounting pin during operation of the lawnmower;

Figs. 2c-d are views according to Fig. 2b, during an exchange of the cutting blade;

Fig. 3a is a perspective view of one embodiment of the mounting pin and the cutting blade;

Figs. 3b-c are views according to 3a, during an exchange of the cutting blade; Figs. 4a-c are perspective views of different embodiments of the cutting blade;

Figs. 5a-b are perspective views of a cutting disk according to a different embodiment of the disclosure;

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted.

Detailed description of the exemplary embodiments

Fig. 1 illustrates a robotic lawn mower 1 comprising, in addition to usual components, such as a motor, a chassis, wheels, etc., a cutting disk 2 with a number of cutting blades 3, mounted on mounting pins 4. The cutting blades 3 are arranged symmetrically in the edge area of the cutting disk 2. The cutting blades 3 are preferably arranged such that they may be rotatable around an axis defined by the mounting pin 4. By being rotatably arranged, they may extend radially outwards, when the cutting disk 2 rotates with a high speed during operation of the robotic lawnmower. Also, the cutting blades 3 may yield if they encounter an obstacle which is too hard or too tough to be cut.

Each cutting blade 3 is provided with at least one, and preferably two, cutting edges 5, which are arranged on at least one longitudinal side 6 of the cutting blade 3. In the embodiments with two cutting edges 5, the lawn mower 1 operates efficiently regardless of the direction of rotation of the cutting disk 2, since there may always be a cutting edge 5 facing forward in either direction of rotation.

Fig. 2a shows an edge portion of the cutting disk 2 with one of the cutting blades 3, a mounting pin 4, which is separable into two joinable parts 4a and 4b in the disclosed embodiment. Both joinable parts 4a, 4b of the mounting pin 4 may be provided with end stoppers 8a, 8b at their outer ends, i. e. the ends facing away from the cutting disk 2, when they are mounted thereon. A biasing means 7 may be arranged around the mounting pin 4, such that one end thereof contacts an end stopper 8b and the other end contacts the cutting disk 2. Typically, the mounting pin 4 and the biasing means 7 are arranged on the cutting disk 2 more or less permanently, although they may sometimes be possible to replace as spare parts, if needed. The cutting disk 2 may comprise holes wherein liners 12 are arranged, through which liners 12 each mounting pin 4 extends. In a practical sense, the liners 12 act as an outer cover of the mounting pins 4, thereby forming a section of each mounting pin 4 with a larger diameter. In the embodiments where the mounting pin 4 comprises two joinable parts 4a, 4b, one part 4b of the mounting pin 4 is, in the disclosed embodiment, provided with a socket, while the second part 4a is provided with a corresponding projection. The socket and projection are designed to interact, e. g. by threads, adhesives, etc., in order to firmly join the parts 4a, 4b. The mounting pin 4 and its socket and projection may have entirely different embodiments than the embodiment shown in the drawings. For example, the projection may extend into a socket arranged closer to the geometrical middle point of the mounting pin, than shown in the drawings.

Another option is that the mounting pin 4 is designed as a rivet, where at least one of the end stoppers 8a, 8b is created by deformation after the mounting pin 4 has been inserted in a hole in the cutting disk 2.

As seen in Figs. 2a-c, the cutting blade 3 is arranged on the mounting pin 4. The mounting pin 4 extends through the liner 12 in the hole in the cutting disk 2. The mounting pin 4 and the liner 12 together extend through an attachment opening 9 in the cutting blade 3, and in this sense, the liner 12 acts as an integral, outer part of the mounting pin 4.

During operation, as shown in Fig. 2b, the cutting blade 3 is arranged to be freely rotatable on the wider part of the mounting pin 4, which e. g. in the embodiment in the figure is the liner 12. In the disclosed embodiment, the cutting blade 3 is arranged below the cutting disk 2, as seen in a normal position of operation. The biasing means 7 is a compression spring in the disclosed embodiment, and it urges the mounting pin 4 upwards, to the position shown in Fig. 2b. In this position the lower end stopper 8a is adjacent to the liner 12, such that the liner 12 defines the outer width of the entity of the mounting pin 4 and liner 12 in this position. There is ample room between the lower end stopper 8a and the underside of the cutting disk 2, to allow the cutting blade 3 to extend outwards by the centrifugal force, when the cutting disk 2 rotates. Also, the cutting blade 3 may easily yield, when it encounters an obstacle, thereby protecting the cutting blade 3 from being damaged. The mounting pin 4 and the liner 12 together extend through a working portion 10 of the attachment opening 9 in the cutting blade 3 during operation of the lawn mower 1 . The width of the liner 12, outside of the mounting pin 4, is accessible to the cutting blade 3 in this position and corresponds to the width of the working portion 10. The cutting blade 3 hereby remains safely mounted on the mounting pin 4 and the liner 12 during the mowing operation.

When the cutting blade 3 needs to be exchanged, the upper end stopper 8b may be pushed downwards, against the bias from the compression spring 7, as shown in Fig. 2c. As an alternative, the lower end stopper 8a may be grasped and pulled downwards, also in a direction against the bias from the compression spring 7. Either way, a narrow section 13 of the mounting pin 4 may extend below the liner 12 and be exposed and accessible below the cutting disk 2 and the lower end of the liner 12. In Fig. 2b, the narrow section 13 may otherwise be covered by the liner 12 extending below the cutting disk 2. In this position the cutting blade 3 and the mounting pin 4 are movable in relation to one another. The cutting blade 3 may be moved mainly in its plane of extent, and the narrow section 13 of the mounting pin 4 may hereby be introduced into a mounting portion 11 of the attachment opening 9. Only the narrow section 13 of the mounting pin 4 is able to enter the mounting portion 11 , since the width of the narrow section 13 corresponds to the width of the mounting portion 11 . The width of the liner 12 matches only the width of the working portion 10. The cutting blade 3 may then be moved relative to the mounting pin 4, such that the narrow section 13 of the mounting pin 4 is guided through the mounting portion 11 towards its outer opening, and the cutting blade 3 is released, as shown in Fig. 2d. Hence the cutting blade 3 may be demounted and mounted manually, without the use of any tools.

When an old cutting blade 3 has been demounted from the mounting pin 4, a new cutting blade 3 may be mounted by moving the cutting blade 3 at the level of the narrow section 13 of the mounting pin 4 and allowing the narrow section 13 to enter the mounting portion 11 of the attachment opening 9. Once the narrow section 13 of the mounting pin 4 has entered the working portion 10 from the mounting portion 11 , the cutting blade 3 and the mounting pin 4 may be mutually moved to guide the mounting pin 4 in the mounting portion 11 towards the working portion. When the mounting pin 4 has reached the working portion 10, the liner 12, which is wider, may enter the working portion 10 in the longitudinal direction of the mounting pin 4. When either end stopper 8a, 8b is released, the biasing means 7 may bring the mounting pin 4 back to the position wherein the narrow section 13 is no longer accessible. Hereby the new cutting blade 3 is securely arranged on the mounting pin 4 and the liner 12, since the wide liner 12 is unable to enter the mounting portion 11 of the attachment opening 9.

In Fig 2d the narrow section 13 of the mounting pin 4 is clearly visible. The provision of the liner 12, as seen in Figs. 2a-d, with a large outer width, extending outside of the mounting pin 4, results in an entity with two different widths, in reality functioning as a single mounting pin 4.

In some embodiments, a narrow section 13 is attained by a notch in an otherwise wider mounting pin 4, reducing the width of the mounting pin 4 in the narrow section 13 to approximately half of that of its wide section, which may be as wide as the outer width of the liner 12, disclosed above. In other embodiments the narrow section 13 may be attained by reducing the width evenly around the circumference of the mounting pin 4, similar to a reduction obtained by turning with a lathe. In such embodiments, the wide liner 12 may be dispensed with, and the narrow section 13 may be arranged, by action of the spring 7, within the thickness of the cutting disk 2, during operation of the robotic lawn mower 1 .

In Figs. 3a-c, the working portion 10 and the mounting portion 11 of the attachment opening 9 in the cutting blade 3 are clearly visible. It is also obvious that the narrow section 13 of the mounting pin 4 fits well in the mounting portion 11 while it is considerably narrower than the width of the working portion 10. The liner 12, or any wider section of the mounting pin 4, which may fit well in the working portion 10, is unable to enter the mounting portion 11 . The mounted cutting blade 3 may hence remain and rotate securely on the liner 12 or a wide section of the mounting pin 4, respectively. Figs. 4a-c disclose a couple of embodiments of the cutting blade 3 and its attachment opening 9. The disclosed embodiments are not intended to be a limiting disclosure, as innumerable variations, as well as combinations, of the embodiments in the figures, that all share the same inventive concept, are possible and are considered as parts of the same invention.

Fig. 4a discloses a basic form of the cutting blade 3. There is one single attachment opening 9 with a mounting portion 11 extending in the same general direction as the longitudinal sides 6 of the cutting blade 3. The length of the mounting portion 11 is widely variable. The working portion 10 is approximately circular, with a diameter slightly larger than that of the liner or wide section 12 of the mounting pin 4 to allow rotation of the cutting blade 3.

The overall strength of the cutting blade 3, the balance of the cutting blade 3 during the mowing and possible yielding to obstacles, as well as the wear on the cutting edges 5 and the inner sides of the attachment opening 9 are all factors to be considered when designing the attachment opening 9, including the working and mounting portions 10, 11.

Fig. 4b discloses another embodiment of the cutting blade 3. The working portion 10 of the attachment opening 9 is oblong and extends mainly in the longitudinal direction of the cutting blade 3. In some embodiments the working portion 10 may be arranged with its longitudinal direction at an angle to the longitudinal direction of the cutting blade 3. Hereby the balance properties and wear may be affected. The mounting portion 11 is curved and opens into the working portion 10 on a longitudinal side thereof. The exact shape of the mounting portion 11 may be dependent on the orientation of the working portion 10 and the balance properties of the cutting blade 3.

Since the mounting portion 11 opens into the longitudinal side of the working portion 10, the oblong working portion 10 has two rounded end zones 15 with integral side walls, i. e. they are free from interruptions. The end zones 15 are probably those zones of the working portion 10 that will be most in contact with the mounting pin 4 or the liner 12, respectively, as the cutting blade 3 is turned outwards by the centrifugal force during rotation of the cutting disk 2. The design of Fig. 4b has the advantages of being able to extend far outwards from the cutting disk 2 and of having a working portion 10 with smooth and strong end zones 15. Also, the wear on the cutting edges 5 will be evenly distributed without reversing the attachment point of the cutting blade 3.

Fig. 4c represents yet another possibility to create further embodiments of the cutting blade 3. Two attachment openings 9 are provided, and they have approximately circular attachment openings 9. The respective mounting portions 11 , extending from opposite transversal sides 14, join the respective working portions 10 from a point closest to a longitudinal side 6. The orientation of the attachment openings 9 is such that the distribution of the weight in the cutting blade 3 will be as even as possible, even when the mounting is switched between the attachment openings 9. Hereby the rotation and yielding of the cutting blade 3 may be as uninhibited as possible. At the same time, the wear on the cutting edges 5 may be evenly distributed by the possibility to switch the mounting between the two working portions 10, and the lifespan of the cutting blade 3 may be maximized.

The embodiments that have been disclosed in the figures and in the text above are merely a few examples, and they may be combined or varied to form a large number of further embodiments, such as cutting blades 3 with two oval working portions 10, cutting blades 3 with two mounting portions 11 parallel with the longitudinal sides, cutting blades 3 with two curved mounting portions 11 , cutting blades with a single, angled mounting portion 11 , and any further combination of these embodiments.

An alternative embodiment of the biasing means 7 is disclosed in Figs. 5a-b. A leaf spring 7 is attached with one end portion 16 on the upper face of the cutting disk 2 for each mounting pin 4. The leaf spring 7 is, at another, free, end portion 17, provided with an opening (not discernible in the figures), through which the mounting pin 4 extends. The upper end stopper 8b may rest on the free end portion 17 during the mowing operation of the lawn mower 1 , and the lower end stopper 8a may remain in such a position that the cutting blade 3 pivots on the liner or the wide section 12 of the mounting pin 4, as seen in Fig. 5a. Pressing the upper end stopper 8b or pulling the lower end stopper 8a against the bias from the leaf spring 7, may expose a narrow section 13 of the mounting pin 4, in a similar manner to the disclosure relating to Fig. 2d.

The leaf spring 7 may, in other embodiments, be arranged in other manners, for example to simply block the cutting blade 3 from reaching the narrow portion 13 of the mounting pin 8, where it may become dismounted. For the narrow portion 13 to be accessible to the mounting portion 11 of the cutting blade 3, the mounting pin 4 may have to be moved temporarily in its longitudinal direction against the bias of the leaf spring 7.

In some embodiments, a central portion of the cutting blade 3, comprising the attachment opening or openings 9, is made of a somewhat softer material than the edges. This may be accomplished e.g. by hardening the outer portions of the longitudinal sides 6, which comprise the cutting edges 5. Another way is by welding harder longitudinal sides 6 to a softer central portion. Regardless of how the constellation of harder cutting edges 5 with a softer central portion is accomplished, the softer central portion of the cutting blade 3 renders the attachment opening 9 tougher and stronger. This aspect is particularly relevant for the durability of the working portion 10 of the attachment opening 9. The sides of the working portion 10 are in contact with the mounting pin 4 during operation of the robotic work tool 1 , and the durability thereof is a factor affecting the overall lifetime of the cutting blade 3.

All of the embodiments in this disclosure may be further modified with a protective structure, or a blade guard, which is arranged on the cutting blade 3. The purpose of the blade guard may be to make the cutting blade 3 easier to handle for the operator. It may lessen the risk of injury to the fingers and hands during the mounting and dismounting of the cutting blade 3, since the cutting blade 3 may be handled by only touching the blade guard. Also, the cutting edges 5 may be protected from damage if the blade guard comprises side projections extending transversally from the longitudinal sides 6 over a limited distance thereof. Hereby the cutting edge 5 may be protected from obstacles that contact the projection and cause the cutting blade 3 to yield and possibly rotate. The blade guard is typically manufactured from a plastic material and may be arranged to cover a transversal side 14, and also parts of the side edges 5. The blade guard is preferably designed such that the opening of the mounting portion 11 is accessible. Hereby the blade guard does not have to be dismounted, in order to mount and dismount the cutting blade 3 on the mounting pin 4, and the risk of injury to the hands or fingers of the user is further considered. The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Claims

Claims A grass cutting blade (3) for a robotic lawn mower (1 ), the cutting blade (3) being elongate with two longitudinal side edges (6) and comprising at least one cutting edge (5) on at least one of the longitudinal side edges (6) of the cutting blade (3) and at least one attachment opening (9) in an area between the longitudinal side edges (6), and the attachment opening (9) has a mounting portion (11 ) and at least one working portion (10), wherein the mounting portion (11 ) extends between the working portion (10) and a side edge (6, 14) of the cutting blade (3), and is open on said side edge (6, 14). The cutting blade (3) according to claim 1 , wherein a largest width of the working portion (10) is larger than a width of the mounting portion (11 ). The cutting blade (3) according to claim 1 or claim 2, wherein both longitudinal sides (6) of the cutting blade (3) are provided with cutting edges (5). The cutting blade (3) according to any of the preceding claims, wherein the cutting blade (3) comprises at least one transversal side edge (14), extending between the longitudinal side edges (6). The cutting blade (3) according to any of the preceding claims, wherein the mounting portion (11 ) of the attachment opening (9) is defined by a pair of mutually opposing mounting portion edges. The cutting blade (3) according to any of the preceding claims, wherein the at least one attachment opening (9) comprises one single working portion (10) and one single mounting (11 ) portion, respectively. The cutting blade (3) according to any of the preceding claims, wherein the mounting portion (11 ) of the attachment opening (9) has elongated sides extending parallel to the longitudinal sides (6) of the cutting blade (3). The cutting blade (3) according to any of the preceding claims, wherein the attachment opening (9) is arranged symmetrically on a center line midway between the two longitudinal side edges (6). The cutting blade (3) according to any of claims 1 to 6, wherein the working portion (10) has elongated sides, and the mounting portion (11 ) is joined to the working portion (10) on an elongated side thereof. The cutting blade (3) according to claim 9, wherein at least one of the mounting portion (11 ) and the working portion (10) is arranged with an angle between a respective axis of extent and the longitudinal side edges (6) of the cutting blade (3). The cutting blade (3) according to any of the preceding claims, wherein the cutting blade (3) comprises two attachment openings (9), arranged at opposing side edges (14) of the cutting blade (3), with their mounting portions (11 ) open towards their respective adjacent side edge of the cutting blade (3). The cutting blade (3) according to claim 11 , wherein the attachment openings (9) are symmetrically arranged about a longitudinal center of the cutting blade (3). The cutting blade (3) according to claim 11 or claim 12, wherein the attachment openings (9) are arranged radially symmetrically around a center of the cutting blade (3). The cutting blade (3) according to any of the preceding claims, wherein each attachment opening (9) has an axis of extent forming an angle to a center line midway between the two longitudinal side edges (6) of the cutting blade (3). The cutting blade (3) according to any of the preceding claims, wherein a protective member is removably arranged on the cutting blade (3), covering at least a part of the transversal side (14) across the mounting portion (11 ), while exposing at least a part of the cutting edge (5). A mounting pin (4), for holding a cutting blade (3) according to any of the preceding claims, the mounting pin (4) having a narrow section (13) with a smallest transverse dimension, a wide section (12) with a larger transverse dimension, and wherein an end stopper (8a, 8b) is arranged at each end of the mounting pin (4). The mounting pin (4) according to claim 15, wherein the mounting pin (4) comprises two joinable parts. The mounting pin (4) according to claim 16, wherein one part of the mounting pin (4) is provided with a socket, and the other part of the mounting pin (4) comprises a projection, which is insertable into the socket. The mounting pin (4) according to any of claims 15 to 17, wherein the narrow section (13) is arranged at a central portion of the mounting pin (4). The mounting pin (4) according to any of claims 15 to 18, wherein the mounting pin (4) comprises a bias spring (7), which is arranged thereon. Combination of at least one mounting pin (4) according to any of claims 15 to 19, and a cutting disk (2) for a robotic lawn mower (1 ), wherein the mounting pin (4) is arranged on the cutting disk (2), approximately perpendicular to a main plane of extension of the cutting disk (2), and a biasing means (7) is arranged on the cutting disk (2) and contacting the mounting pin (4), such that the mounting pin (4) is movable in its longitudinal extent against a bias from the biasing means (7). Combination of at least one cutting blade (3), according to any of claims 1 to 14, and at least one mounting pin (4) according to any of claims 15 to 19, wherein the mounting pin (4) is arranged on a cutting disk (2) for a robotic lawn mower (1 ), which cutting disk (2) has a main plane of extension, and the cutting blade (3) is arranged to be rotatable on the wide section (12) of the mounting pin (12) around a rotational axis defined by a longitudinal extent of the mounting pin (4), which is extending in a direction across the main plane of extension of the cutting disk (2), the mounting pin (4) and the cutting blade (3) are mutually movable in the direction of the rotational axis, and the cutting blade (3) is manually slideable past the narrow section (13) of the mounting Pin (4). Combination according to claim 21 , wherein the cutting blade (3) is slideable past the narrow section (13) of the mounting pin (4) by a motion transversal to the rotational axis. Combination according to claim 21 or claim 22, wherein the mounting pin (4) is movable in its axial direction by manual force. Combination according to any of claims 21 to 23, wherein a biasing means (7) is arranged on the cutting disk (2) and the mounting pin (4) and the biasing means (7) are mutually movable in the longitudinal extent of the mounting pin (4) against a bias from the biasing means (7). Combination according to claim 24, wherein the biasing means (7) contacts at least one of the end stoppers (8a, 8b) on the mounting pin (4). Combination according to any of claims 21 to 25, wherein the cutting blade (3) is arranged below the cutting disk (2), as seen in an operating position. Combination according to any of claims 21 to 25, wherein the cutting blade (3) is arranged above the cutting disk (2), as seen in an operating position. Robotic lawn mower (1 ) including a cutting blade (3) according to any of claims 1 to 14, or a mounting pin (4) according to any of claims 15 to 19 or a combination according to any of claims 20 to 28. Mounting method of a cutting blade (3) according to any of claims 1 to 14 on a cutting disk (2) of a robotic lawn mower (1 ), comprising a mounting pin (4) according to any of claims 15 to 19, wherein the method comprises the following steps: the mounting pin (4) is moved in its axial direction, such that its narrow section (13) is accessible, the cutting blade (3) is brought to the mounting pin (4) with its open mounting portion facing the mounting pin (4) and the cutting blade (3) is held with its main plane of extent at the level of the narrow section (13) of the mounting pin (13), the cutting blade (3) is moved, at the same level, relative to the mounting pin (4), such that the narrow portion (13) is introduced first into the mounting portion (11 ) and then into the working portion (10), whereafter the mounting pin (4) is moved in its axial direction, such that its wide section (12) is arranged at the level of the cutting blade (3) in the working portion (10). Mounting method according to claim 30, wherein the mounting pin (4) is moved against a bias in at least one of its axial directions.